Computational design of segmented concrete shells made of post-tensioned precast flat tiles

This paper introduces a novel structural concept for free-form shells, in which the shape is decomposed into flat concrete tiles to be assembled sequentially with the help of falseworks. All tiles can be prefabricated in the shop with an adaptable and reusable molding system. Once the assembly is completed, the tiles are post-tensioned through a network of cables to minimize tension and avoid detachment. The top surface can finally be completed with an in situ cast layer that fills the gaps and activates the entire shell behavior. In contrast, the bottom surface maintains a jagged aesthetics. The paper presents the automatic pipeline supporting the computational design of these shells, from an input shape to its fabrication. The segmentation of the input shape is guided by a field-aligned quad mesh derived from the principal stresses of the thin shell. The tiles are flattened individually and extruded along the normal of the best-fitting plane. In this configuration, only edge midpoints of adjacent tiles share a contact point. Thus, forces can mainly flow along the tiles' cross directions. The best configuration of cable paths and pre-loads is found by solving a constrained optimization problem exploiting a reduced model of the shell as a network of beams. Six different input shapes are tested to demonstrate the applicability of the proposed design method. The working hypotheses are validated through a higher-resolution nonlinear Finite Element Analysis. The fabrication pipeline is assessed utilizing a reduced-scale 3D-printed replica.